We report on the first observation of the beauty baryon Λb in an exclusive decay channel at the CERN pImage collider. Using 4.7 pb−1 of muon data collected in the 1988/89 collider runs we reconstruct 16±5 Λb's in the decay mode Λb→J/ψΛ above a background of 9±1 events, corresponding to a significance of about five standard deviations. We measure the Λb mass to be mΛb=5640±50±30 MeV/c2. Using the beauty cross-section measured by UA1 we deduce for the product of the production fraction and branching ratio fΛb Br (Λb→J/ψΛ)=(1.8±1.0)×10-10. Our sample contains three-muon event in which the beauty particle opposite to the Image is tagged by the third muon. We also observe an indication of a signal in the decay channel B0→J/ψK0* with a significance of three standard deviations.